Migrate to go1.12 to simplify our cmd/http package (#7302)

Simplify the cmd/http package overall by removing
custom plain text v/s tls connection detection, by
migrating to go1.12 and choose minimum version
to be go1.12

Also remove all the vendored deps, since they
are not useful anymore.

cmd/http/deadlineconn.go

@@ -0,0 +1,77 @@
+/*
+ * Minio Cloud Storage, (C) 2017 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package http
+
+import (
+	"net"
+	"time"
+)
+
+// DeadlineConn - is a generic stream-oriented network connection supporting buffered reader and read/write timeout.
+type DeadlineConn struct {
+	QuirkConn
+	readTimeout            time.Duration // sets the read timeout in the connection.
+	writeTimeout           time.Duration // sets the write timeout in the connection.
+	updateBytesReadFunc    func(int)     // function to be called to update bytes read.
+	updateBytesWrittenFunc func(int)     // function to be called to update bytes written.
+}
+
+// Sets read timeout
+func (c *DeadlineConn) setReadTimeout() {
+	if c.readTimeout != 0 && c.canSetReadDeadline() {
+		c.SetReadDeadline(time.Now().UTC().Add(c.readTimeout))
+	}
+}
+
+func (c *DeadlineConn) setWriteTimeout() {
+	if c.writeTimeout != 0 {
+		c.SetWriteDeadline(time.Now().UTC().Add(c.writeTimeout))
+	}
+}
+
+// Read - reads data from the connection using wrapped buffered reader.
+func (c *DeadlineConn) Read(b []byte) (n int, err error) {
+	c.setReadTimeout()
+	n, err = c.Conn.Read(b)
+	if err == nil && c.updateBytesReadFunc != nil {
+		c.updateBytesReadFunc(n)
+	}
+
+	return n, err
+}
+
+// Write - writes data to the connection.
+func (c *DeadlineConn) Write(b []byte) (n int, err error) {
+	c.setWriteTimeout()
+	n, err = c.Conn.Write(b)
+	if err == nil && c.updateBytesWrittenFunc != nil {
+		c.updateBytesWrittenFunc(n)
+	}
+
+	return n, err
+}
+
+// newDeadlineConn - creates a new connection object wrapping net.Conn with deadlines.
+func newDeadlineConn(c net.Conn, readTimeout, writeTimeout time.Duration, updateBytesReadFunc, updateBytesWrittenFunc func(int)) *DeadlineConn {
+	return &DeadlineConn{
+		QuirkConn:              QuirkConn{Conn: c},
+		readTimeout:            readTimeout,
+		writeTimeout:           writeTimeout,
+		updateBytesReadFunc:    updateBytesReadFunc,
+		updateBytesWrittenFunc: updateBytesWrittenFunc,
+	}
+}